This invention relates to heat exchangers, particularly of the type known as heat regenerators and recuperators. While not so limited, the preferred use of the invention is in connection with industrial furnaces such as, for example, open-hearth furnaces, coke ovens, soaking pits, batch-type and continuous heating, reheating, heat treating and melting furnaces, as they relate to the steel, aluminum, glass, refractory and other industries. In such industries exchangers are sometimes referred to as air pre-heaters.
To refer, for the purpose of background, to but one prior use of regenerators, it is a common use to provide in a billet reheating furnace a number of burner units that are designed and arranged to serve alternatively as burners and as regenerators. As burners, the units supply the necessary heat in the form of combustible fuel gas to the furnace, as regenerators they remove hot waste gas from the furnace. Thus, for a given set of units, one unit while serving as a burner is fed clean preheated air from the second unit, which air has been heated to a desired temperature from the hot waste gas removed from the furnace. Some of the features of this burner arrangement can be seen from U.S. Pat. Nos. 4,358,268 and 4,756,688. The design and arrangement just described is not only expensive from a "Machinery Cost Standpoint " but also from a maintenance point of view, not to mention the very elaborate piping-valve-control system cost and in some instances the necessity of arranging the valves of the regenerator on the "hot" side or end of the units.
In addition to the aforesaid U.S. Patents, prior U.S. Pat. Nos. 1,688,700, 3,207,493 and 4,349,069 may serve as background for the present invention. Briefly commenting on these patents in reverse order, the 069 patent is of interest, among other things, in illustrating the use of valves at the "hot end" of a regenerator. The 493 patent shows in combination with a furnace chamber, the alternate operation of a two single flow path regenerator, while the 700 patent illustrates an air regenerator having two single flow paths in two separate chambers and having valves at both the "hot" and "cold" ends of each chamber. The designs represented by each of these last referred to prior art patents possess and are subject to more or less the same disadvantages and objections noted above as to the designs of the U.S. Pat. No. 4,358,268 and U.S. Pat. No. 4,756,688 patents. In addition, some of the designs, namely the 700 patent, require a purging of the system before the change from the hot input flow path to the cold input flow path and the necessary interruption in the operation of the regenerator when this is accomplished.